[PATCH] nfs: force drop_nlink if we have a delegation during REMOVE

[Roberto Bergantinos Corpas <rbergant@redhat.com>]

commit bd4928ec799b ("NFS: Avoid changing nlink when file removes and
attribute updates race") avoids races on attribute cache with any
inflight RPC that may modify inode attributes (and gencount) during
i.e. REMOVE.

However it does not take into account that REMOVE may trigger
a delegation return which also advances gencount (via the attribute
refresh during delegation return), and in that case the gencount
mismatch is not due to an inflight RPC that already reflected the
removal.

If nlink is 1 and we have a delegation before REMOVE, we should force
the drop to ensure the VFS delivers the expected FS_DELETE_SELF
notification.

This fixes LTP/inotify04 failure after bd4928ec799b.

Fixes: bd4928ec799b ("NFS: Avoid changing nlink when file removes and attribute updates race")
Reviewed-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Roberto Bergantinos Corpas <rbergant@redhat.com>
---
 fs/nfs/dir.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 2402f57c8e7d..bc6bbf434a21 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1937,13 +1937,13 @@ static int nfs_dentry_delete(const struct dentry *dentry)
 }
 
 /* Ensure that we revalidate inode->i_nlink */
-static void nfs_drop_nlink(struct inode *inode, unsigned long gencount)
+static void nfs_drop_nlink(struct inode *inode, unsigned long gencount, bool force)
 {
 	struct nfs_inode *nfsi = NFS_I(inode);
 
 	spin_lock(&inode->i_lock);
 	/* drop the inode if we're reasonably sure this is the last link */
-	if (inode->i_nlink > 0 && gencount == nfsi->attr_gencount)
+	if (inode->i_nlink > 0 && (force || gencount == nfsi->attr_gencount))
 		drop_nlink(inode);
 	nfsi->attr_gencount = nfs_inc_attr_generation_counter();
 	nfs_set_cache_invalid(
@@ -1961,7 +1961,7 @@ static void nfs_dentry_iput(struct dentry *dentry, struct inode *inode)
 	if (dentry->d_flags & DCACHE_NFSFS_RENAMED) {
 		unsigned long gencount = READ_ONCE(NFS_I(inode)->attr_gencount);
 		nfs_complete_unlink(dentry, inode);
-		nfs_drop_nlink(inode, gencount);
+		nfs_drop_nlink(inode, gencount, false);
 	}
 	iput(inode);
 }
@@ -2556,10 +2556,11 @@ static int nfs_safe_remove(struct dentry *dentry)
 	trace_nfs_remove_enter(dir, dentry);
 	if (inode != NULL) {
 		unsigned long gencount = READ_ONCE(NFS_I(inode)->attr_gencount);
+		bool force_drop = nfs_have_read_or_write_delegation(inode) && inode->i_nlink == 1;
 
 		error = NFS_PROTO(dir)->remove(dir, dentry);
 		if (error == 0)
-			nfs_drop_nlink(inode, gencount);
+			nfs_drop_nlink(inode, gencount, force_drop);
 	} else
 		error = NFS_PROTO(dir)->remove(dir, dentry);
 	if (error == -ENOENT)
@@ -2852,7 +2853,7 @@ int nfs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 			new_dir, new_dentry, error);
 	if (!error) {
 		if (new_inode != NULL)
-			nfs_drop_nlink(new_inode, new_gencount);
+			nfs_drop_nlink(new_inode, new_gencount, false);
 		/*
 		 * The d_move() should be here instead of in an async RPC completion
 		 * handler because we need the proper locks to move the dentry.  If
-- 
2.53.0